Neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease are becoming popular with the recent increase in the old-age population, and there is an increasing demand for medicines for preventing and/or treating such neurodegenerative diseases.
Recently, it is said that one factor causing those diseases is the hypofunction of mitochondrial complexes. Mitochondria exist in all animal cells, while participating in the production of energy necessary for cell activities via electron-transfer system. However, mitochondria and mitochondrial genes are easily damaged by oxidative stress deriving from dysfunction of the electron-transport system (for example, radical attack of reactive oxygen species, etc.), resulting in energetic hypometabolism and cell degeneration. In particular, brain cells require high energy consumption, in which, therefore, mitochondria existing are more easily degenerated, thereby resulting in so-called brain electron-transport mitochondrial disorders to be caused by anomalous mitochondrial transmission with aging [e.g., Proceeding of National Academy of Sciences, USA, 91, 8731-8738 (1994), etc.].
Ubiquinone, which is a particular quinone compound, is indispensable as the coenzyme for oxidation-reduction in electron-transport systems. Derivatives having the quinone skeleton of ubiquinone have been produced.
As a compound having a mitochondrial function activating effect and a nerve growth factor production enhancing effect, known is idebenone; 6-(10-hydroxydecyl)-2,3-dimethoxy-5-methyl-1,4-benzoquinone [e.g., JP-A-56-97223, U.S. Pat. No. 4,436,753, JP-A-3-81218, U.S. Pat. No. 5,059,627, Biochemical and Biophysical Research Communications, 125, 1046-1052 (1984), etc.].
On the other hand, the following bicyclic or tricyclic quinone compounds are known.
1) JP-A-59-128348 discloses a compound of the formula: ##STR2##
which has a prostaglandin biosynthesis inhibiting effect and is useful as a non-steroidal, anti-inflammatory analgesic.
2) Journal of the American Chemical Society, 112, 1987-1905 (1990) discloses a compound of the formula: ##STR3##
3) Chemical Society Perkin Transactions, 1, 2979-2988 (1990) discloses compounds of formulae: ##STR4##
which have an anti-tumoral activity.
4) Australian Journal of Chemistry, 29, 179-190 (1976) discloses a compound of the formula:
##STR5## R.sup.1 R.sup.2 R.sup.3 H OMe H H H OMe OMe H H H OMe OMe H Me H H H Me
Studies of medicines for inhibiting mitochondrial dysfunctions, which are for treatment of Alzheimer's disease, etc., are being made, while being essentially directed to antioxidants. It is now desired to develop compounds which are different from the above-mentioned known compounds in their chemical structures but which have an excellent mitochondrial function activating effect and are satisfactory as active ingredients in medicines.